Messages in this thread Patch in this message | | | Date | Mon, 10 Jul 2023 10:46:25 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] ftrace: Fix possible warning on checking all pages used in ftrace_process_locs() |
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On Tue, 11 Jul 2023 05:29:58 +0800 Zheng Yejian <zhengyejian1@huawei.com> wrote:
> As comments in ftrace_process_locs(), there may be NULL pointers in > mcount_loc section: > > Some architecture linkers will pad between > > the different mcount_loc sections of different > > object files to satisfy alignments. > > Skip any NULL pointers. > > After 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"), > NULL pointers will be accounted when allocating ftrace pages but > skipped before adding into ftrace pages, this may result in some > pages not being used. Then after 706c81f87f84 ("ftrace: Remove extra > helper functions"), warning may occur at: > WARN_ON(pg->next); > > So we may need to skip NULL pointers before allocating ftrace pages. > > Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions") > Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com> > --- > kernel/trace/ftrace.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index 3740aca79fe7..5b474165df31 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -6485,6 +6485,16 @@ static int ftrace_process_locs(struct module *mod, > if (!count) > return 0; > > + p = start; > + while (p < end) { > + /* > + * Refer to conments below, there may be NULL pointers, > + * skip them before allocating pages > + */ > + addr = ftrace_call_adjust(*p++); > + if (!addr) > + count--; > + }
My main concern about this is the added overhead during boot to process this. There's 10s of thousands of functions, so this loop will be 10s of thousands. I also don't like that this is an unconditional loop (meaning it executes even when it is unnecessary to do so).
> /* > * Sorting mcount in vmlinux at build time depend on > * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in
How about something like this?
-- Steve
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index b24c573934af..acd033371721 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6474,6 +6474,7 @@ static int ftrace_process_locs(struct module *mod, struct ftrace_page *start_pg; struct ftrace_page *pg; struct dyn_ftrace *rec; + unsigned long skipped = 0; unsigned long count; unsigned long *p; unsigned long addr; @@ -6536,8 +6537,10 @@ static int ftrace_process_locs(struct module *mod, * object files to satisfy alignments. * Skip any NULL pointers. */ - if (!addr) + if (!addr) { + skipped++; continue; + } end_offset = (pg->index+1) * sizeof(pg->records[0]); if (end_offset > PAGE_SIZE << pg->order) { @@ -6551,12 +6554,24 @@ static int ftrace_process_locs(struct module *mod, rec->ip = addr; } - /* We should have used all pages */ - WARN_ON(pg->next); - /* Assign the last page to ftrace_pages */ ftrace_pages = pg; + /* We should have used all pages unless we skipped some */ + if (pg->next) { + WARN_ON(!skipped); + while (ftrace_pages->next) { + pg = ftrace_pages->next; + ftrace_pages->next = pg->next; + if (pg->records) { + free_pages((unsigned long)pg->records, pg->order); + ftrace_number_of_pages -= 1 << pg->order; + } + kfree(pg); + ftrace_number_of_groups--; + } + } + /* * We only need to disable interrupts on start up * because we are modifying code that an interrupt
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